Teutonic Knights conquered the Dzialdowo region and built a castle in the early 14th century. A wing of the castle still remains. The new settlement near the castle founded by Mikołaj z Karbowa and named Soldov was granted town privileges on 14 August 1344 by the Grand Master Ludolf König. The name Dzialdoff was first written on a 1409 map during the Polish–Lithuanian–Teutonic War.
References:Visby Cathedral (also known as St. Mary’s Church) is the only survived medieval church in Visby. It was originally built for German merchants and inaugurated in 1225. Around the year 1350 the church was enlarged and converted into a basilica. The two-storey magazine was also added then above the nave as a warehouse for merchants.
Following the Reformation, the church was transformed into a parish church for the town of Visby. All other churches were abandoned. Shortly after the Reformation, in 1572, Gotland was made into its own Diocese, and the church designated its cathedral.
There is not much left of the original interior. The font is made of local red marble in the 13th century. The pulpit was made in Lübeck in 1684. There are 400 graves under the church floor.